Dust outflows from starburst galaxies

We present submillimeter SCUBA images of the nearby, starburst galaxies NGC 253, NGC 4631 and M82 (primarily at wavelengths of 450 and 850 mu m). The edge-on orientation of our targets. in conjunction with the resolution of t he instrument (15 " FWHM at 850 mu m), allows us to probe the optically-obs cured centre and resolve the minor-axis superwind from the main disk. For N GC 253 and M82, we detect a blight source, a few hundred parsec in diameter , which corresponds to the central starburst. In the case of M82, the bi-lo bal nature of the central source is suggestive of a torus or ring. We confirm the existence of a dust outflow along the minor axis of M82 and make a similar (but somewhat more tentative report) for the other two galax ies NGC 253 and NGC 4631. The scale-size of the 'vertical' features is 0.7- 1.2 kpc. A mass of 10(6-7)M (.) is infered for the outflowing grains in M82 . We conclude that this amount of grain material could either have accrued from an inflow along the disk (e.g. a bar) or, if the lower mass limit appl ies, have been synthesized by massive stars in the starburst. The ejected g rains are probably travelling close to the escape velocity of the host gala xy and assuming, hypothetically, that they do manage to breach the halo, we expect superwinds to expel up to 10% of the dust residing in interstellar disks into the intergalactic medium.